Myogenic tissue culture systems provide extremely useful model systems in which to study gene regulation during tissue formation. We have isolated and characterized a variety of muscle-specific and house-keeping genes that are differentially expressed during myogenesis. These include three different actin genes (alpha cardiac, alpha skeletal and beta cytoplasmic actins) and the myosin light chain 1-3 gene. All but the beta cytoplasmic actin gene are expressed only in muscle tissue. The cis acting sequence elements involved in the tissue specific regulated expression of these genes have been characterized and we are currently in the process of identifying proteins that interact with these regulatory regions to modulate gene expression. Mutational analysis of factor binding sites coupled with in vivo and in vitro transcriptional studies allow one to determine the nature of the various regions in these cis regulatory sequence elements. PC12 cells undergo neuronal differentiation in response to nerve growth factor (NGF). We have isolated the complete cDNA and corresponding gene for an mRNA that is specifically induced 50-80 fold by NGF in PC12 cells. Antibodies to the polypeptide, prepared with LacZ fusions to different ORFs in the cDNA, define a protein of 72,000 daltons which appears to be a marker for cells in the CNS that respond to NGF. Preliminary studies with the gene promoter suggest NGF induces transcription. The cis regulatory elements of the gene responsive to NGF induction are under study. Using defined oligo nucleotide probes to highly conserved regions in the myosin heavy chain polypeptide from all the nonmuscle myosins sequenced to date we have isolated the yeast myosin gene. The role of the yeast myosin in the life cycle of yeast is under study. Gene replacement studies with mutant and chimeric myosin gene, from Acanthamoeba or the higher vertebrates will give information on the structure- function relationships of the various myosins and a means to map functionally important domains in myosin and actin.